Hybrid electric vehicles utilizing both an electric motor/generator and an internal combustion engine as power sources have an onboard controller programmed to vary use of each of the engine and motor/generator during different driving conditions. Generally, a controller receives input signals from vehicle sensors that monitor current operating conditions. The controller executes various algorithms to determine a desired functional mode of the powertrain. The ability of the powertrain to function as desired is dependent in part upon the speed and accuracy of adaptation to changing operating conditions.